1. Field of the Invention
The present invention relates to a decoding method and a decoding apparatus for decoding an image taken and coded by a plenoptic camera, a storage medium in which a decoding program is stored, and an electronic camera having a characteristic of a shape of an optical system.
2. Description of the Related Art
FIG. 25 shows a focus function of a normal camera. Light collected by a focus lens 121 and other optical systems (not shown) such as a zoom optical system is projected onto an imaging device 127 disposed in an image plane 121F. As shown by an arrow 121B, a position of the focus lens 121 can be changed along an optical axis 121H with respect to the image plane 121F. The position of the focus lens 121 is used in processing firmware of the camera during control of auto focus (AF) and managed by a discrete numeric value. The numeral 121A of FIG. 25 designates the discrete “focus value”.
In the case where the optical system of the normal camera includes a zoom optical system, or in the case where the normal camera has the complicated optical system, the focus lens 121 is formed by a lens group including plural lenses. In such cases, the focus value 121A indicates a changeable and controllable overall state of the lens group.
The camera lens is based on the fact that an image of an object on a plane is formed on a plane. The plane on which the image is formed on the image plane 121F without defocus by the focus lens 121 disposed with a predetermined focus value is referred to as “best object plane”. When a subject is located on a best object plane 121D, the image is formed on the imaging device 127 while the camera is completely brought in focus. A subject distance 121E which is a distance from the image plane 121F to the best object plane 121D can be changed by changing the focus value 121A. The focus value 121A and the subject distance 121E correspond to each other one-on-one.
Actually a depth of field 121G exists according to an allowable range of the defocus, and the light is projected onto the imaging device 127 while the camera is substantially brought in focus even if an object plane 121J deviates from the best object plane by the depth of field 121G.
FIG. 26A shows the case in which an image is taken with the normal camera. A user manipulates the auto focus or manual focus to bring the camera into focus on a subject X. The manipulation corresponds to a situation in which the best object plane 121D is matched with a subject plane of the subject X by moving the focus lens 121 in the optical axis direction 121H. FIG. 26A shows a state in which the focus lens 121 is moved to a certain focus value 121A to match the best object plane 121D with the subject surface of the subject X. When a release button is pressed in this state of things, the light from the subject X is projected onto the imaging device 127 through the focus lens 121 while the camera is brought in focus.
On the other hand, in the plenoptic camera, the light from the subject X is projected onto a microlens array 125 as shown in FIG. 26B. That is, the microlens array 125 is placed in the image plane 121F of FIG. 26B, and the imaging device 127 is disposed at the back of the microlens array 125. Through the structure of the plenoptic camera, various light rays K1, K2, and K3 projected from the subject X onto the microlens array 125 are separated by an individual microlens 125A and projected onto a part 127A of the imaging device 127. Accordingly, information on the image formed by the part 127A of the imaging device includes information on a direction of the light ray. On the other hand, because the light from the subject X is projected onto the microlens array 125, the imaging result of the imaging device 127 includes positional information indicating from which position of the subject X the light ray is incident.
Thus, the image information (light field image) which is the imaging result of the imaging device in the plenoptic camera includes the information (light ray information) on the light ray in the space. The plenoptic camera can sample four-dimensional light ray information as described above.
For example, U.S. Pat. No. 6,097,394 discloses a technique of coding the light ray information (light field image information). In the technique, a vector quantization method is adopted to improve a decoding rate. Vector coding data is decoded by referring to and outputting an index in a code book (dictionary data) unlike predictive coding adopted in Moving Picture Experts Group (MPEG) in which an access to decoded data becomes complicated.